I immediately turned off the car. When I restarted it, everything returned to normal, and the car is running fine. Since I'm planning to go on a long trip soon, I contacted the Nissan dealership.
The first person I spoke to over the phone without seeing the car told me that it can happen sporadically. I asked them to inspect the vehicle because diagnosing it over the phone didn't seem right to me. They replied that they don't have any available slots to see the car (which is disappointing considering I bought the car from them six months ago). In an other dealership connected the car to a PC but didn't find any anomalies. They suggested further analysis of the battery or a possible engine electronic update. However, they also didn't have availability.
So, I went to a third center, and they scheduled an appointment for next week. They will keep the car for two days for proper checks.
I am Italian, and on several Italian forums/websites, some people have reported similar, if not identical, issues. Most of them resolved the problem by either updating the firmware or replacing the battery. Others were told that these are sporadic bugs that occur during the car's startup when something doesn't start correctly, resulting in the error message. If the message disappears after turning off and on the car, it's not a real problem.
Of course, I want to have the car checked. In the meantime, has anyone had similar experiences?